In fabrication of integrated circuits (ICs), it is important to test the individual circuit chip die while they are still attached in a semiconductor wafer and to test the packaged integrated circuit devices. In many testing applications, the tests must be performed over temperature. Accordingly, automated test systems are commonly outfitted with temperature control systems which can control the temperature of the wafer or device under test.
In some testing systems, such as wafer probers, the wafer is held on a temperature-controlled chuck, and electrical stimulus signals are applied to the circuits on the wafer, circuit response signals are detected via an array of electrical contact probes brought into contact with the wafer. The temperature of the chuck and, therefore, the temperature of the wafer, can be controlled by a heater and/or heat sink integrated into the chuck and by temperature-controlled fluid circulated through the chuck. Such systems are manufactured and sold by Temptronic corporation of Sharon, Mass.
In other systems, packaged ICs are tested over temperature by applying the electrical stimulus signals and receiving response signals via the IC package pins. The device under test (DUT) is held in a socket on a platform, and the test signals are routed to the pins via the socket. In one such system, the THERMOSTREAM(trademark) system manufactured and sold by Temptronic Corporation, a temperature-controlled steam of air is directed onto the DUT to control the temperature of the DUT during testing.
As wafers become larger, and as circuits become smaller and more densely integrated, positioning tolerances for these test systems become smaller. Accordingly, it is becoming increasingly important that the support system on which the DUT or wafer is supported be mechanically stable and rigid and also extremely flat, since mechanical flaws such as distortions in the platform would adversely affect the positioning capability of the system. This is particularly important in temperature-controlled test systems, since mechanical systems tend to distort and warp over temperature. Particularly at high temperature, distortions in the support platform can become so great that substantial inaccuracies in testing can result.
The present invention is directed to a mechanically stable temperature-controlled platform for supporting a workpiece such as a wafer or a packaged IC DUT during testing which eliminates these drawbacks. In accordance with the invention, there is provided a thermal platform and method for supporting a workpiece. The platform includes a top surface assembly on which the workpiece can be mounted. A thermal plate made of a porous thermally conductive material is located in thermal communication with the top surface assembly. A fluid inlet allows a temperature-controlled fluid, for example, air, to enter the thermal plate and propagate through the porous material of the thermal plate. A temperature controller controls the temperature of the fluid to control the temperature of the workpiece.
In one embodiment, the workpiece is a semiconductor wafer on which are formed one or more integrated circuits. In another embodiment, the workpiece is a packaged integrated circuit.
In one embodiment, the thermal platform is contained within a test system for testing the workpiece. For example, the test system can be a wafer prober machine or a packaged IC device handler. At least a portion of the temperature controller can be externally located such that it is connected to the test system via a hose. The temperature controller includes a fluid source for providing the temperature-controlled fluid to the test system via the hose. The one particular embodiment, the temperature controller includes a fluid heater located in the test system for heating the fluid.
In one embodiment, the porous thermally conducted material comprises a sintered metal. In another embodiment, the material comprises reticulated foam. The thermally conducted material can include copper. It can also comprise a carbon and/or graphite foam.
The thermal platform can include a layer of channels adjacent to the thermal plate which facilitate the flow of fluid through the thermal plate. The channels can be arranged in a radial spiral pattern to facilitate the flow of fluid radially from a central portion of the thermal plate to its perimeter. The channels can be formed in one or more surfaces of the thermal plate. Alternatively, the channels can be formed in a separate convector plate located adjacent to the thermal plate.
In another aspect, the invention is directed to an apparatus and method for testing an integrated circuit. The apparatus includes a test circuit in which the integrated circuit is supported. A temperature control is coupled to the test system. The temperature control system includes a fluid source for providing a fluid to the test system in thermal communication with the integrated circuit. A controller in the temperature control controls the temperature of the fluid to control the temperature of the integrated circuit. A fluid heater for heating the fluid is located within the test system.
In one embodiment of this aspect of the invention, the test system is a wafer prober. In another embodiment, the test system is a packaged integrated circuit device handler. Accordingly, the IC can be part of an IC wafer or it can be packaged in an IC package.